const obj = {
    name:"oumasyu",
    age:18,
    hobbies:["sing","rap","dance"]
}
// 设计来迭代对象的属性的
for(let k in obj){
    console.log(k,obj[k]);
}
// 数组也是对象，把数组看待成下标为key的可迭代对象
const arr = [1,2,3,4,5,6];
// key是下标
for(let key in arr){
    console.log(key,arr[key]);
}